Metal soaps are finding widespread use in the plastics industry especially in the processing of thermoplastics such as polyvinylchloride, polyethylene, polypropylene, polystyrene, ABS resins and others in the form of stabilizers, lubricants and release agents. These metal soaps are used in granular form since this enhances their ease of handling and processing.
It is known to produce metal soaps by means of a dual reaction. In this process the metal soaps are formed by precipitation from aqueous solutions of the alkali or ammonium salt of fatty acids caused by the addition of aqueous solutions of metal salts. Another widely used method is the neutralization reaction. According to German Pat. No. 8 60 210 this process employs an emulsion of the liquid fatty acid containing ammonia, alkylol amine or other useful nitrogen bases which is reacted with an aqueous suspension of metal oxides or metal hydroxides. Another process, especially for the manufacture of lead soaps is described in the German Auslegeschrift 10 68 238. According to this method, electrolyte-free normal lead salt of fatty acids having from 8 to 30 carbon atoms is obtained by mixing an aqueous suspension of lead oxide, whose temperature lies below the melting point of the fatty acid, with either molten, colloidial, flakes or pulverized fatty acid; such reaction taking place in the absence of catalysts or wetting agents. The metal soaps obtained by the above mentioned process constitute extremely fine, light and voluminous powders which are very prone to forming fine dusts. This means that their production and handling is subject especially to the constant danger of dust explosions as well as to health hazards arising from the toxic metal soap dust. This situation jeopardizes the use of these generally, essential, metal soaps, since very expensive protective measures have to be utilized. Another considerable disadvantage of metal soaps in powder form is found in their unsatisfactory flow characteristics. This does not permit their being handled in bulk which would otherwise allow for their economic transport and storage, as well as their use in automated proportioning equipment.
Many efforts have been made to produce dust-free metal soaps. However, none of the known processes described hereinafter for the production of metal soaps have attained technical importance. Thus it is known, according to the German Pat. No. 15 68 283, that granular mixed soaps can be produced from water insoluble acids and two or more bivalent metals. In this process a molten mixture of an organic, water insoluble acid and one of its dibasic metal salts is used. This liquid mixture is combined dropwise with an aqueous preparation containing an oxide or hydroxide of at least one additional bivalent metal which forms a salt of high melting point with the molten, water insoluble fatty acid. This process is restricted to the manufacture of specific metal soap combinations. Furthermore, the metal soaps thus produced proved generally unsatisfactory with regard to their practical application.
German Auslegeschrift 12 79 658 describes a method for the granulation of powdery masses, such as metal soaps, which is carried out in the aqueous phase with the use of difficult to dissolve or insoluble organic granulating aids at temperatures above 60.degree. C. German Auslegeschrift 15 42 058 describes a method for the granulating of production aids, including metal soaps, used as additives for the plastics industry. In this process the powders which are to be granulated are combined with a binding agent having a hydrocarbon radical and the mass is then heated to above the melting point of the binding agent, during which time the mass is vigorously agitated. This is followed by less intense agitation while the reaction product cools. These processes used binding agents e.g. granulating aids, which limit the general applicability of such granulates considerably, since the nature of such agglutinants often causes increased material costs.
Long established methods for the production of dust-free products are tableting, extruding, flaking and spraying. These shaping or compacting processes, which are carried out in the sinter or melting region of the material, can be applied to metal soaps only with the assistance of melting aids so as to reduce thermal or oxidative deterimental effects to a tolerable level. Furthermore, these processes use binding agents which adds considerable equipment costs as well as the attendant disadvantage discussed above. If this process could be used without binding agents, if such were possible, a compacted granulate would result. The reason why these processes never attained commercial importance can be found in the unsatisfactory dispersability and reactivity of the dense metal soaps thus obtained.
The object of the present invention is the preparation of a pure metal soap granulate, or mixtures thereof, in which the production is accomplished in a combined operation to eliminate high energy costs and without the use of binding agents or melting aids, resulting in a product of high reactivity and good dispersability.